Signal data in synthetic aperture radar (SAR) systems or synthetic aperture lidar (SAL) systems are often processed to generate a range-Doppler map. In a SAR system, the Doppler centroid (i.e., the Doppler frequency corresponding to the center of the radar beam) is required to optimize the clutter-to-noise ratio (CNR) of the SAR image map and to accurately determine the target location.
Doppler centroid values calculated directly from the ancillary SAR system data may contain significant errors when the azimuth beam width of the system is relatively narrow in comparison with the azimuth beam pointing accuracy. If the errors are within a fraction of the azimuth beam width, the errors have sometimes been resolved by estimating the Doppler centroid from the azimuth spectra of the data.
However, in some systems, the error of the Doppler centroid may be as large as several times the pulse repetition frequency (PRF). This is often the case with, for example, synthetic aperture lidar systems and spaceborne imaging radar systems operating at high frequency bands. In such cases, it is also necessary to account for the Doppler ambiguity. The target location error (TLE) caused by Doppler ambiguity may be significant in some applications. It is often necessary to determine the Doppler ambiguity in SAR and SAL systems to satisfy both CNR and TLE accuracy and performance requirements. A need therefore exists for systems and methods for accurately determining the Doppler and range ambiguity in radar, lidar and acoustic system data.